However, for reasons of space and on account of the necessary decorrelation of the radiators from one another, the configuration and the number of the antennae under the same cover are limited. Likewise, for example official regulations regarding the dimensions of the cover (as an attachment, overall height especially) and structural requirements from the designer must be taken into account.
With regard to the overall height of the cover, problems arise in particular from the actual design and the positioning of the mobile communication antennae, and here especially of the radiator for the 900 MHz range. The antenna should have an all-round characteristic in the horizontal radiated field pattern and would optimally be configured as a monopole. If the overall height of a monopole of this kind and that of the other structural components of the arrangement to be positioned one above the other on the vehicle roof was now added together, then a dimension would result for the entire arrangement which is greater than the 70 mm permissible according to regulations.
Even if the conventional folded or similarly structured configuration of the radiator for the 900 MHz range appears to achieve, overall, the necessary electrically effective height, this still leaves a great deal to be desired. This is because, to the same extent that the geometrical dimensions of the structure are reduced, reductions in RF function and quality also generally become increasingly difficult to avoid.
Corresponding motor vehicle antennae, frequently provided with a fin-like covering cap, are known from a large number of prior publications.
DE 10 2009 051 695 A1 for example describes an antenna arrangement in which the vertical board comprising an antenna is arranged above a base plate. A solution which is comparable in this respect is also known from DE 20 2005 017 773 U1. The horizontal boards generally comprise a through-opening merely for the connection to the electronics, through which opening a lug or tab of the respective board, which is vertically arranged and provided with an antenna arrangement, can project beneath the plane of the horizontal board.
US 2006/0038726 A1 describes a vertical monopole antenna, the lower rim or lower edge of which extends as far as the surface of a base or of a pedestal supporting the entire antenna.
The same also applies to the antenna arrangement known from US 2007/0103374 A1.
In contrast, the object of the invention is to provide more scope for improvements in the configuration, and thus the effectiveness, of specific antennae beneath the cover, in particular the mobile communication antennae, by means of design measures with regard to individual elements of the roof-mounted antenna arrangement.
The object is achieved according to the invention in accordance with the features set out in claim 1. Advantageous embodiments are specified in the dependent claims.
In the invention, the space beneath the cover which can be used for positioning a vertical board part having antenna structures extends downwards towards the base plate, while retaining the outer dimensions of the cover. In this case, the ground reference can be specified directly in the design of the base plate. For example, the vertical surface available for the antenna increases in height by 5 mm or more, depending on the dimensions which would otherwise arise from the thickness of the horizontal board and the space beneath which is required for the components.
In the context of the invention, it is therefore proposed that the base plate, i.e. the pedestal or the base, which receives and supports the entire antenna, comprises a recess in the base region thereof, so that the lower edge of the vertical board is arranged beneath the base surface which points upwards and is formed by the bottom of the base plate.
In this respect, the invention in part also refers to skeletonising the base plate, i.e. a measure by means of which the desired opening is produced, so that the vertical board comprising an antenna arrangement can be positioned even lower.
Thus, when skeletonising the base plate is also provided as explained above, further or additional gains in height for the configuration of an antenna structure are made compared with the prior art. The skeletonising is possible in part as far as the planar part of the base plate which is required for arranging the means, which are known per se, for mounting and retaining the attachment above the opening in the roof surface. Thus, a frame is retained from the remaining portion of the base plate, which frame provides the border for the assembly with the cover, and a circumferential seal, and to which the board portions comprising the antennae and the circuit can be fixed. In the variant of the invention having a skeletonised base plate, the metal roof surface of the vehicle can directly serve as the ground plane for the antennae.
The invention provides the option of either installing the vertical board comprising the antenna structure lower down in order to reduce the overall height of the roof-mounted antenna arrangement to equal the outer height of the fin cover, or of enlarging upwards the surface of the vertical board beneath the cover while maintaining a predetermined cover size. Last but not least, when implementing the arrangement according to the invention, savings can also be made at least with respect to the board material and, when including the base plate, also with respect to the proportion of metal, together with a reduction in weight.